The present invention generally relates to improved particulates and methods of using such particulates in subterranean applications. More particularly, in certain embodiments, the present invention relates to particulates comprising a cementitious material and a filler material, methods of preparing those particulates, and associated methods of using the particulates in subterranean applications.
Hydraulic fracturing is a process commonly used to increase the flow of desirable fluids, such as oil and gas, from a portion of a subterranean formation. Hydraulic fracturing operations generally involve introducing a treatment fluid commonly referred to as a fracturing fluid into a subterranean formation at a pressure sufficient to create or enhance one or more fractures in the formation. Enhancing a fracture includes enlarging a pre-existing fracture in the formation. The fracturing fluid may comprise particulates, often referred to as “proppant” that are deposited in the fractures. The proppant may function to prevent the fractures from fully closing upon the release of pressure, forming conductive channels through which fluids may flow to (or from) the well bore.
Another process that involves the use of particulates is gravel packing. A “gravel pack” is a term commonly used to refer to a volume of particulate materials (such as sand) placed into a well bore to at least partially reduce the migration of unconsolidated formation particulates into the well bore. Gravel packing operations commonly involve placing a gravel pack screen in the well bore neighboring a desired portion of the subterranean formation, and packing the surrounding annulus between the screen and the subterranean formation with particulate materials that are sized to prevent and inhibit the passage of formation solids through the gravel pack with produced fluids. In some instances, a screenless gravel packing operation may be performed.
Conventional particulates included as proppant and/or gravel in subterranean treatment fluids include, but are not limited to: sand; bauxite; ceramic materials; glass materials; polymer materials; TEFLON® (polytetrafluoroethylene) materials; nut shell pieces; seed shell pieces; fruit pit pieces; wood; composite particulates; cured resinous particulates comprising nut shell pieces, seed shell pieces, inorganic fillers, and/or fruit pit pieces; and combinations thereof. Conventionally, composite particulates that may be used comprise a binder and a filler material wherein suitable filler materials include silica, alumina, fumed carbon, carbon black, graphite, mica, titanium dioxide, meta-silicate, calcium silicate, kaolin, talc, zirconia, boron, fly ash, hollow glass microspheres, solid glass, and combinations thereof.
The specific gravity of conventional particulates is often so high as to make it difficult to suspend the particulates in unviscosified treatment fluids. As a result, viscosifiers are often added to treatments fluids such as fracturing fluids and gravel packing fluids. Such viscosifiers may be expensive and may have an adverse impact on production stimulation and well completion operations. One example of an adverse impact may be that at the high concentrations of viscosifier needed to suspend traditional high strength particulates, the viscosifier may contribute to a reduction in the conductivity of the subterranean formation. The suspension of conventional particulates in a treatment fluid may also raise the overall density of the treatment fluid to an undesirable level. When the treatment fluid is injected into a well bore, e.g., during a gravel packing operation, the high hydrostatic pressure applied to the well bore may result in unwanted fracturing of the subterranean formation.
While some conventional particulates such as walnut hulls and their composite particulates have a relatively low specific gravity, those particulates are generally unable to withstand significant closure stresses over time at elevated subterranean temperatures. This may be a disadvantage when using low strength particulates as proppant in a fracturing fluid since it allows the cracks to close, thereby reducing the conductivity of the fracture. Similarly, a variety of lightweight particulates formed of thermoplastic materials including polyolefins, polystyrene divinylbenzene, polyfluorocarbons, polyethers etherketones and polyamide imides are commercially available. However, when these particles are exposed to temperatures above about 150° F., they often soften and deform, and may not be suitable in all well bores.
There may also be difficulties associated with obtaining and/or manufacturing some conventional particulates. For instance, sand proppants are usually only mined in certain areas of the world and may not be available globally. Bauxite ceramic proppant, which may have a desirably higher crush strength than sand, is a man-made material that is typically sintered at high temperatures, e.g., temperatures of about 1500° C. Particulates such as bauxite which must be cured at high temperatures may require the use of specialized sintering kilns. These processes consume large amounts of energy. Bauxite may also be more expensive than sand. Proppants comprising a binder comprised of resin are known and may have an advantageously lower density than bauxite, but may not be cost effective. Transporting sand proppants to job sites may be difficult and expensive.